ADHD & Serotonin Differences

The three main components of ADHD are hyperactivity, impulsivity, and inattention. As outlined in Section #2, a person can have the first two, the last one, or a combination of all three. 

First we’ll look at the baseline traits of Neurotype I from Part 7. Then I’ll outline possible contributing factors for 1) hyperactivity and impulsivity as well as 2) inattention criteria from the DSM-5.

Baseline Traits of Neurotype I / Neurodivergence

  • Higher cortical arousal: Mind is stimulated more naturally by acetylcholine, may process stimuli faster, thoughts may race, can get overstimulated or have trouble shaking hyper-focus in times of stress (as cortisol suppresses serotonin, which normally modulates acetylcholine.)
  • Prefers concrete details over abstracts in conversations: Likes less ambiguity, straightforward approach, someone saying outright what they want or how they feel, gives more consideration to facts over interpretations.
  • Sensitive to polychronic time: Minutes and hours feel untrackable without timer, can get lost in a task, prefers to multitask.
  • More motivated by tangible rewards: Needs to know or see end results, may feel dread instead of excitement while anticipating something, have trouble accomplishing long-term goals without milestone rewards.
  • Lean more toward serotonergic traits versus dopaminergic ones: Per Fisher's Builder personality: cautious, persistent, loyal, fond of rules and facts, and orderly.
  • Overly sensitive to negative outcomes: May be less impulsive and may rely more on aversive motivation to avoid punishments, negative situations, and feeling bored.
  • Struggle more in the absence of serotonin versus the absence of dopamine: May experience anxious depressive episodes, have trouble controlling emotions, and struggle with stepping away from a hyper-focus.

Hyperactivity and Impulsivity
(Serotonin Deficit)

There was a 2015 study out of the University of Calcutta (E Banerjee and K Nandagopal) where the authors noted that serotonin can help mitigate some of the symptoms of ADHD. Specifically, it helped with hyperactivity and impulsivity. (Source)

Serotonin’s role in moderating hyperactivity and impulsivity is pretty straightforward. While there are multiple pathways for dopamine, it generally has a green light effect. We’ve seen this in studies about task assessment and action. One of the most recent studies was released in October 2020. (Source) The authors discussed how serotonin helped to inhibit dopamine release when there was more uncertainty. (From an evolutionary standpoint, this interchange could potentially stop a person from walking into a literal lion’s den. But that’s purely my informal guess.)

Dopamine isn’t bad, especially in moderation. We’ve seen this in the research behind the wanting and liking pathways. (Source) Dopamine can push you to pursue the things you want and help activate the reward system for the things you like doing. It helps us find things fascinating and makes us want to try new things. But when it’s not kept in check, the system can go haywire. Dopamine-seeking behaviors take over which can result in hyperactivity and impulsivity. You can get stuck in a loop of pursuing something you want. And without serotonin to help mitigate it after a reward is reached, the satisfaction can fade quickly and have you craving more.

This may help explain why such powerful stimulants are used for ADHD. If the body has access to dopamine more for a longer amount of time, it may not keep acting in ways that will boost it. (For reference, some of these behaviors include talkativeness, attention-seeking, acting rashly, and giving into addictive habits.)

A big part of the feedback I get when talking about serotonin deficits in ADHD is that SSRIs don’t improve all of the symptoms of ADHD. The Calcutta study by E Banerjee and K Nandagopal acknowledged this too. (Source) But it’s important to keep in mind that SSRIs do not create serotonin, they just help to keep serotonin that's already present in the system around for longer. (Source) But if a person is not getting enough from their diet (source), if there's not enough Vitamin D to help synthesize it (source), or even if the person isn’t able to move around enough during the day to promote brain plasticity (source), it can lead to a brain serotonin deficiency. This is an oversimplification of how the serotonin system works. But it helps to illustrate how a serotonin deficit isn’t solely treatable with SSRIs.

Here’s a disclaimer though to anyone outside of the medical realm reading this: Do not take medication or supplements without a doctor’s guidance. We know that too much serotonin can lead to serotonin syndrome, which can ultimately have severe or even fatal results. We also know that certain supplements can’t pass the blood-brain barrier, so instead it can mess with bodily processes that serotonin is a part of. This is why with any hormone or neurotransmitter it's important to have balance. You don't want to take too much of it, you don't want to have too little. Each one has an important and complex role in the body, so balance is key.

Inattention
(Serotonin Difference)

There are two types of inattention that people with ADHD report having — 

  • Getting distracted by everything around them and
  • Falling into a hyperfocus that they can’t step away from.

The E Banerjee and K Nandagopal (University of Calcutta study) could not show that serotonin helped immediately with inattention. (Source) And dopamine is one way we keep attention. So it’s understandable why a dopamine deficit is considered in ADHD. But I want to talk about another stimulant that those with higher cortical arousal rely significantly on: acetylcholine.

There was another study on how involuntary eye movements helped to connect cortical arousal and attention. The authors noted, per their reading of the data, that "arousal increases the chances of an involuntary, but well-learned, response to a powerful stimulus. But the extent of that influence is based on individual variation in generalization to other responses. And that connection remains unknown." (Source)

This relates to the 2014 ADHD marker test that was developed by researchers at Tel Aviv University. They noted that people with ADHD "had more involuntary eye movements than the control group. But the introduction of certain stimulants helped improve performance in the task by normalizing the suppression of involuntary eye movements to the average level of the control group." (Source)

While inattention is less established than hyperactivity and impulsivity, there may be two serotonin deficient reactions that can explain it. (Research previously outlined the possibility of a dopamine deficiency in people with ADHD. One of the reasons is because of a dopamine transporter gene variant seen in people with ADHD. This is why incorporating research into human behavior is important. If the studies on anticipation and dopamine sensitivity can be replicated in people with ADHD, it may help explain these variants in a biological sense. (Source) Especially because acetylcholine helps modulate dopamine. (Source))

Acetylcholine helps us process initial stimuli and focus on task-relevant stimuli. (Source) And serotonin can help modulate it — acting as a switching board for attention. In cases where serotonin isn’t present, a person can fall into a hyperfocus. We’ve seen similar research on this for ASD. (Source) But in loud and hectic environments, a mind with higher levels of cortical arousal may be reacting to everything around it.

Again, it is not my intention to oversimplify the way hormones and neurotransmitters work. The body is highly complex, and each has a much bigger function in our reactions, long-term health, and overall processes. But for the sake of helping future research, I believe it’s important to combine day-to-day experiences (such as common school and desk work environments) with how these neurotransmitters may react.

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